U.S. patent number 10,180,077 [Application Number 15/173,991] was granted by the patent office on 2019-01-15 for moving-vane angle of attack probe.
This patent grant is currently assigned to Meggitt (UK) Limited. The grantee listed for this patent is Meggitt (UK) Limited. Invention is credited to Alan Waddington.
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United States Patent |
10,180,077 |
Waddington |
January 15, 2019 |
Moving-vane angle of attack probe
Abstract
A moving-vane angle of attack probe is provided. The moving-vane
angle of attack probe comprises: a vane having opposed first and
second vane surfaces that define a leading edge and a trailing
edge, the first and second vane surfaces, each extending between
the leading edge and the trailing edge; a first vane opening
located on the leading edge; at least one exhaust opening; a vane
conduit extending between the first vane opening and the exhaust
opening such that the first vane opening and the exhaust opening
are in fluid communication, the vane conduit defining at least an
interior chamber between the first and second vane surfaces; and a
pitot-tube located within the interior chamber such that in use it
receives air that enters the interior chamber via the first vane
opening.
Inventors: |
Waddington; Alan (Surrey,
GB) |
Applicant: |
Name |
City |
State |
Country |
Type |
Meggitt (UK) Limited |
Dorset |
N/A |
GB |
|
|
Assignee: |
Meggitt (UK) Limited (Dorset,
GB)
|
Family
ID: |
53785094 |
Appl.
No.: |
15/173,991 |
Filed: |
June 6, 2016 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20160356175 A1 |
Dec 8, 2016 |
|
Foreign Application Priority Data
|
|
|
|
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Jun 8, 2015 [GB] |
|
|
1509884.1 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01P
13/025 (20130101); G01P 5/06 (20130101); G01P
5/165 (20130101); F01D 9/02 (20130101); F01D
21/003 (20130101) |
Current International
Class: |
G01P
5/06 (20060101); G01P 13/02 (20060101); F01D
21/00 (20060101); G01P 5/165 (20060101); F01D
9/02 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1275947 |
|
Jan 2003 |
|
EP |
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2847672 |
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May 2004 |
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FR |
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WO01/67115 |
|
Sep 2001 |
|
WO |
|
WO-2005054874 |
|
Jun 2005 |
|
WO |
|
Other References
Search Report corresponding to the European Application No.
16172987.6-1568 dated Oct. 18, 2016, twelve pages. cited by
applicant .
Search Report corresponding to GB 1509884.1 dated Dec. 14, 2015,
four pages. cited by applicant.
|
Primary Examiner: Allen; Andre J
Attorney, Agent or Firm: Kilpatrick Townsend &
Stockton
Claims
The invention claimed is:
1. A moving-vane angle of attack probe comprising: a vane having
opposed first and second vane surfaces that define a leading edge
and a trailing edge, the first and second vane surfaces, each
extending between the leading edge and the trailing edge; a first
vane opening located on the leading edge; at least one exhaust
opening; a vane conduit extending between the first vane opening
and the exhaust opening such that the first vane opening and the
exhaust opening are in fluid communication, the vane conduit
defining at least an interior chamber between the first and second
vane surfaces; and a pitot-tube located within the interior chamber
such that in use it receives air that enters the interior chamber
via the first vane opening.
2. A moving-vane angle of attack probe according to claim 1,
wherein at least a portion of the vane conduit comprises an upper
interior chamber wall, a lower interior chamber wall, a first
interior chamber sidewall and a second interior chamber sidewall
which together define the interior chamber.
3. A moving-vane angle of attack probe according to claim 2,
wherein the exhaust opening is located on the trailing edge, and
wherein at least one of the upper interior chamber wall, lower
interior chamber wall, first interior chamber sidewall and second
interior chamber sidewall extends to the trailing edge.
4. A moving-vane angle of attack probe according to claim 1,
wherein the first vane opening is a slot opening configured to
extend along the leading edge.
5. A moving-vane angle of attack probe according to claim 2,
wherein the pitot-tube comprises: a first shielding wall extending
substantially between the first and second sidewalls of the
interior chamber; a second shielding wall extending substantially
between the first and second sidewalls of the interior chamber,
wherein the first shielding wall and the second shielding wall are
spaced apart from each other to define a first sensor opening
therebetween; a rear wall extending between the first shielding
wall and the second shielding wall, and substantially between the
first and second sidewalls of the interior chamber; and a first
pressure conduit located between the first sensor opening and the
rear wall, wherein the first pressure conduit is configured to
transmit a pressure between the first and second shielding
walls.
6. A moving-vane angle of attack probe according to claim 5,
wherein the first sensor opening faces the first vane opening.
7. A moving-vane angle of attack probe according to claim 5,
wherein first and second bypass channels are defined between the
first shielding wall and the lower interior chamber wall, and the
second shielding wall and the upper interior chamber wall
respectively, and wherein the bypass channels are configured such
that, in use, a portion of the air that enters the interior chamber
is directed along the first and second bypass channels without
entering the pitot-tube.
8. A moving-vane angle of attack probe according to claim 1,
wherein the leading edge is at an angle to an axis of rotation of
the vane.
9. A moving-vane angle of attack probe according to claim 1,
wherein the vane conduit tapers inwardly as it extends from the
vane opening.
10. A moving-vane angle of attack probe according to claim 1,
further comprising at least a first static pressure system, said
first static pressure system comprising at least a first static
pressure port that opens through one of the first and second vane
surfaces, and a first static pressure conduit in fluid
communication with the first static pressure port.
11. A moving-vane angle of attack probe according to claim 10,
wherein the first static pressure system further comprises a first
manifold internal to the vane, wherein the first static pressure
port is configured to open into the first manifold, wherein the
first static pressure conduit is configured to open into the first
manifold, and wherein the first static pressure conduit is
configured to transmit a static pressure in the first manifold.
12. A moving-vane angle of attack probe according to claim 11
wherein the first static pressure system further comprises a second
static pressure port, and wherein the first static pressure port
opens through the first vane surface, and the second static
pressure port opens through the second vane surface, and wherein
the second static pressure port opens into the first manifold.
13. A moving-vane angle of attack probe according to claim 10,
further comprising a second static pressure system, wherein the
second static pressure system comprises a third static pressure
port that opens through one of the first and second vane surfaces,
and a second static pressure conduit in fluid communication with
the third static pressure port.
14. A moving-vane angle of attack probe according to claim 10,
wherein at least the first static pressure port is located in a
depression in the first or second vane surface, and wherein
preferably each static pressure port is located in a separate
depression in the first or second vane surface.
15. A moving-vane angle of attack probe according to claim 1,
further comprising an electronics assembly for taking angle of
attack and/or pressure readings, the electronics assembly having an
external housing, wherein the vane is connected to the electronics
assembly external housing by a pivot, and wherein the vane is
configured to rotate relative to the electronics assembly external
housing.
16. A moving-vane angle of attack probe according to claim 15,
further comprising a counterweight system located inside the
electronics assembly external housing, wherein the counterweight
system is fixedly connected to the vane through the pivot, and
wherein the first conduit is configured to transmit the pressure
between the first and second shielding walls through the pivot and
to a first pressure sensor located on the counterweight system in
the electronics assembly external housing.
17. A moving-vane angle of attack probe comprising: a vane having
opposed first and second vane surfaces that define a leading edge
and a trailing edge, the first and second vane surfaces, each
extending between the leading edge and the trailing edge; a first
depression formed in the first vane surface; and a first static
pressure system, said first static pressure system comprising at
least a first static pressure port configured to open through said
first vane surface in the region of said first depression, and a
first static pressure conduit configured to transmit a static
pressure; wherein the first depression is configured such that, in
use, air flowing over said first vane surface undergoes a change in
pressure in the region of said first static pressure port.
18. A moving-vane angle of attack probe according to claim 17,
wherein the first static pressure system further comprises a first
manifold internal to the vane, wherein the first static pressure
port is configured to open into the first manifold, and wherein the
first static pressure conduit is configured to open into the first
manifold and configured to transmit a static pressure in the first
manifold.
19. A moving-vane angle of attack probe according to claim 18,
further comprising a second depression formed in the second vane
surface, wherein the first static pressure system further comprises
a second static pressure port configured to open through said
second vane surface in the region of said second depression, and
wherein the second depression is configured such that, in use, air
flowing over said second vane surface undergoes a change in
pressure in the region of said second static pressure port.
20. A moving-vane angle of attack probe according to claim 17,
further comprising a third depression in either the first or second
vane surface, and a second static pressure system, said second
static pressure system comprising at least a third static pressure
port configured to open through either the first or second vane
surface in the region of said third depression, wherein the third
depression is configured such that, in use, air flowing over said
first or second vane surface undergoes a change in pressure in the
region of said third static pressure port.
Description
FIELD OF THE INVENTION
The present invention is directed to a moving-vane angle of attack
probe.
DESCRIPTION OF THE RELATED ART
Conventionally, aircraft have been fitted with separate air data
sensors for measuring pitot-static pressure, angle of attack and
temperature. This results in a fairly complex installation, with
each sensor requiring power, data communications and in the case of
pitot-static systems, pneumatic connections. To reduce system
complexity, multi-function probes have been produced which perform
the functions of two or more of these sensors, usually with
integral measurement and processing capability.
In particular, moving-vane angle of attack probes have been
integrated with pitot-static pressure sensors by mounting a
conventional pitot-tube on the top of a moving vane. Examples of
such probes may be found in U.S. Pat. No. 4,672,846 A, U.S. Pat.
No. 6,679,112 BB, U.S. Pat. No. 6,817,240 BB, and U.S. Pat. No.
7,155,968 BB. Alternatively, probes with separate pitot-static and
vane subassemblies have been proposed, as described in U.S. Pat.
No. 6,941,805 BB. In both these cases, the integrated sensors have
a large surface area and require significant de-icing power to
maintain functionality of the probe.
An alternative approach has been to add additional pressure ports
to a conventional pitot-static probe and use differential pressure
measurements to calculate angle of attack, as described in U.S.
Pat. No. 4,378,696 A. These probes also require considerable
de-icing power and additionally have the disadvantage that the
angle of attack measurements are not independent of the
pitot-static pressure measurements, which could result in a common
mode failure affecting both the air data system and the stall
warning system.
It is therefore desirable to produce a multi-sensor probe that
overcomes the various shortcomings of the state of the art.
SUMMARY OF INVENTION
In accordance with a first aspect of the present invention, a
moving-vane angle of attack probe is provided, the probe
comprising: a vane having opposed first and second vane surfaces
that define a leading edge and a trailing edge, the first and
second vane surfaces, each extending between the leading edge and
the trailing edge; a first vane opening located on the leading
edge; at least one exhaust opening; a vane conduit extending
between the first vane opening and the exhaust opening such that
the first vane opening and the exhaust opening are in fluid
communication, the vane conduit defining at least an interior
chamber between the first and second vane surfaces; and a
pitot-tube located within the interior chamber such that in use it
receives air that enters the interior chamber via the first vane
opening.
The present inventor has identified that a reduction in the
de-icing power required by a multi-sensor probe may be achieved by
reducing the total surface area of the probe. The inventor then
recognised that, for angle of attack and total pressure sensing
probe, this could be achieved by positioning a pitot-tube, which
requires significant de-icing power, inside the body of a
moving-vane. The present inventor also identified that this further
contributed to reducing the required de-icing power as the heat
that radiates outwards as the pitot-tube is de-iced can now be used
to de-ice the surrounding vane.
Preferably the interior chamber is defined by an upper interior
chamber wall, a lower interior chamber wall, first interior chamber
sidewall and second interior chamber sidewall, and more preferably
at least one and preferably each of these walls extends from the
opening in the leading edge of the vane. While preferable, it will
be appreciated that the opening, subsequent vane conduit and
internal chamber may be defined in numerous different ways.
Embodiments in which the interior chamber walls define the opening
on the leading edge of the vane promote a smooth flow of air back
into the interior chamber such that the air sampled by the
pitot-tube accurately reflects the air flow towards the probe.
In some embodiments, the exhaust opening is located on the trailing
edge. An exhaust on the trailing edge ensures that air flowing out
of the exhaust opening will not affect the angle of attack reading
produced by the probe. While this is preferable, other embodiments
are foreseen, including for example embodiments in which first and
second exhaust openings are located on the first and second vane
surfaces.
Preferably, the upper interior chamber wall, lower interior chamber
wall, first interior chamber sidewall and second interior chamber
sidewall each extend from the opening on the leading edge of the
vane to the exhaust opening on the trailing edge so as to define
the interior chamber across the whole of the length of the
vane.
Preferably the opening in the leading edge of the vane is a slot
opening configured to extend along the leading edge. While
preferable, other embodiments are foreseen in which, for example,
the opening is substantially cylindrical.
Similarly, it is preferable that the exhaust opening is also a slot
opening, which is configured to extend along the trailing edge.
In particularly preferable embodiments, the pitot-tube comprises: a
first shielding wall extending substantially between the first and
second sidewalls of the interior chamber; a second shielding wall
extending substantially between the first and second sidewalls of
the interior chamber, wherein the first shielding wall and the
second shielding wall are spaced apart from each other to define a
first sensor opening therebetween; a rear wall extending between
the first shielding wall and the second shielding wall, and
substantially between the first and second sidewalls of the
interior chamber; and a first pressure conduit located between the
first sensor opening and the rear wall, wherein the first pressure
conduit is configured to transmit a pressure between the first and
second shielding walls.
The above described pitot-tube construction may be considered to be
a "two-dimensional" shielded pitot-tube. A two-dimensional
pitot-tube refers to a pitot-tube that does not exhibit rotational
symmetry and, more specifically, one which is described by
extrusion of a two-dimensional design. The present inventor
identified that, because the vane is configured to rotate about an
axis, the rotational symmetry of a conventional shielded pitot-tube
is no longer necessary since the direction of air flow will lie in
a plane that is parallel to the vane. Any direction of air flow
other than this would cause the vane to rotate until the direction
of air flow was once again parallel with this plane. Embodiments
which use the two-dimensional pitot-tube design have a simplified
construction when compared to embodiments which use spherical
shielded pitot-tubes. It is also preferable that the pitot-tube be
shielded in this way so that the total pressure measurement is
insensitive to local angle of sideslip. Here, total pressure refers
to the air pressure between the two shielding walls when air
flowing into the pitot-tube hits the rear wall of the sensor, and
is a combination of the static pressure or freestream pressure and
the dynamic pressure.
It is further preferable that the first sensor opening faces the
first vane opening. This arrangement allows air to flow directly
through the vane opening and into the sensor opening without any
significant interaction with the vane. While preferable, other
embodiments are foreseen in which the sensor opening does not
directly face the vane opening.
It is also preferable that first and second bypass channels are
defined between the first shielding wall and the lower interior
chamber wall, and the second shielding wall and the upper interior
chamber wall respectively, and wherein the bypass channels are
configured such that, in use, a portion of the air that enters the
interior chamber is directed along the first and second bypass
channels without entering the pitot-tube.
The provision of bypass channels between the shielding walls and
the interior chamber walls ensures that the sensor opening does not
sample the turbulent air that flows immediately beside the interior
chamber walls. Instead, the sensor opening samples only a middle
portion of the air flowing through the interior chamber. While
preferable, embodiments are foreseen which do not feature bypass
channels.
Preferably, the pitot-tube further comprises first and/or second
drain holes located between the first sensor opening and the rear
wall, the drain holes extending through the first and/or second
vane surface. The drain holes act to remove ingested water and
melted ice from the pitot-tube.
So that the vane can travel at speeds in excess of Mach 1, it is
preferable that the leading edge is at an angle to an axis of
rotation of the vane, and in particular, it is preferable that the
vane is in a swept back configuration, as opposed to a swept
forward configuration.
The provision of a swept vane results in a cross-flow along the
edge of the vane. With the vane opening located on the leading
edge, this results in air flowing into the opening at an angle to
the direction of travel. The inventor identified that it is
therefore preferable that the vane conduit tapers inwardly as it
extends from the vane opening. By providing that the vane conduit
tapers inwardly, the leading edge effectively curves smoothly into
the opening, and the air flow into the interior chamber may be
straightened so that the pitot-tube samples air which correctly
reflects the direction and speed of the air flowing towards the
vane. In these embodiments, the leading edge may transition into
one or both of the upper or lower interior chamber walls on one or
both sides of the opening, so that the air is guided into the
interior chamber as smoothly as possible.
Preferably, a distance between the upper and lower interior chamber
walls decreases as the upper and lower interior chamber walls
extend away from said vane opening, and preferably the upper and
lower interior chamber walls taper inwardly as they extend from
away from said vane opening. While only the leading edge on the
upstream side of the opening need curve or taper to correct for
cross-flow, it is preferable that both sides taper.
The inventor also identified that it is preferable that the
integrated probe be able to provide static pressure measurements as
well as total pressure and angle of attack measurements. Therefore,
in some embodiments, the pitot-tube is a pitot-static tube. While
this could take the form of a conventional pitot-static tube housed
within the interior chamber, in some particularly preferable
embodiments, the probe further comprises at (least a first static
pressure system, said first static pressure system comprising at
least a first static pressure port that opens through one of the
first and second vane surfaces, and a first static pressure conduit
in fluid communication with the first static pressure port. More
preferably, the static port is in fluid communication with a first
manifold internal to the vane, and the first static pressure
conduit is configured to open into the first manifold and to
transmit a static pressure in the first manifold.
By providing one static pressure port on one side of the vane, it
is possible that, if the rotation of the vane lags behind a change
in wind direction, a defect due to the increased or decreased
pressure on that side of the vane could affect the accuracy of the
static pressure measurement. It is therefore preferable that the
probe further comprises a second static pressure port in the other
vane surface, the second static pressure port being in fluid
communication with the first manifold such that the first manifold
is connected to the atmosphere on either side of the vane. With
this configuration, the pressure in the first manifold is an
average of the pressures on either side of the vane, and so a
defect due to the vane lagging behind a change in wind direction is
cancelled out.
In static pressure probes, redundancy is desirable, and so
particularly preferable embodiments further comprise a second
static pressure system. The second static pressure system may be
formed similarly to that of the first, with either one or two
static pressure ports and preferably with a second manifold.
The present inventor has identified that, in embodiments which
feature a static pressure system, a defect in the static pressure
measurements will exist which is caused by the change in air
pressure as it flows around the vane, thereby affecting the air
pressure in the region of the static pressure port. He has further
identified that this defect can be corrected for by shaping the
vane. It is therefore preferable that at least the first static
pressure port is located in a depression in the first or second
vane surface, and further preferable that each static pressure port
is located in a separate depression in the first or second vane
surface. While it is preferable that each pressure port is located
in a separate depression, it is also possible that multiple ports
could be located in a single, larger depression in the surface of
the vane.
In particularly preferable embodiments, the depression is a groove
which runs up the first or second vane surface. The depression in
the surface of the vane changes the pressure of the air in the
region of the static pressure port as the air flows over the vane.
The precise dimensions of the depression can be selected so that,
at all velocities, the air pressure in the region of the static
pressure port substantially reflects the freestream pressure
(ignoring other pressure defects that will be discussed in more
detail later).
As previously mentioned, the moving-vane angle of attack probe of
the present invention advantageously reduces the de-icing power
required. In particularly preferable embodiments, the de-icing is
performed by at least one heat source disposed between the first
and second vane surfaces. The at least one heat source is able to
perform the de-icing of both the external surface of the vane and
the pitot-tube and static pressure systems in an efficient manner.
Preferably, the heat source comprises a foil heater and/or a
ceramic heater, and further preferably the at least one heat source
includes a first heater located between the first and second vane
surfaces, wherein the first heater extends across substantially all
of the area of the first or second vane surface and/or a second
heater located proximate the interior chamber.
In further preferable embodiments, the moving-vane angle of attack
probe further comprises an electronics assembly for taking angle of
attack and/or pressure readings, the electronics assembly having an
external housing, wherein the vane is connected to the electronics
assembly external housing by a pivot, and wherein the vane is
configured to rotate relative to the electronics assembly external
housing.
In particularly preferable embodiments, a counterweight system is
located inside the electronics assembly external housing, the
counterweight system being fixedly connected to the vane through
the pivot. The counterweight system prevents the weight of the vane
itself affecting the angle of attack measurement, and is
advantageously contained in the electronics assembly for a compact
design.
In some embodiments, the first conduit is configured to transmit
the first pressure through the pivot and to a first pressure sensor
located in the electronics assembly external housing. While
preferable, it is foreseen that other embodiments will exist that
have, for example, a pressure sensor located in the vane
itself.
In particularly preferable embodiments, the first pressure sensor
is located on the counterweight system. Such embodiments are
particularly preferable for two reasons. Firstly, it is preferable
to have the pressure sensor fixed relative to the vane so as to
simplify communication of air pressure. Secondly, the weight of the
total pressure sensor can be used to contribute to the total weight
of the counterweight system.
In some embodiments, the electronics assembly further comprises a
computer fixedly mounted in the electronics assembly housing for
processing the sensor measurements. While preferable, it is also
foreseen that embodiments exist in which the sensor measurements
are communicated outside of the probe for processing.
Preferably the first pressure sensor communicates via at least one
of a slip ring and a rotary transformer. In embodiments in which a
computer is present, preferably the first pressure sensor
communicates with the computer via the slip ring and/or rotary
transformer
In embodiments which include static pressure systems, it is
preferable that the first static pressure conduit transmits a first
static pressure to a first static pressure sensor located in the
electronics assembly external housing, and, if present, that the
second static pressure conduit transmits a second static pressure
to a second static pressure sensor located in the electronics
assembly external housing in a way similar to the above first
pressure conduit.
According to a second aspect of the present invention, a
moving-vane angle of attack probe comprises a vane having opposed
first and second vane surfaces that define a leading edge and a
trailing edge, the first and second vane surfaces, each extending
between the leading edge and the trailing edge; a first depression
formed in the first vane surface; and a first static pressure
system, said first static pressure system comprising at least a
first static pressure port configured to open through said first
vane surface in the region of said first depression, and a first
static pressure conduit configured to transmit a static pressure;
wherein the first depression is configured such that, in use, air
flowing over said first vane surface undergoes a change in pressure
in the region of said first static pressure port.
In these embodiments, the moving vane angle of attack probe
provides angle of attack measurements and static pressure
measurements. These embodiments also provide the same benefits of
reduced de-icing power as the first aspect by allowing for a
reduced surface area and efficient arrangement of features. These
embodiments further include at least one pressure system which has
a static pressure defect corrected by a shaped vane surface.
Specifically, the correction is performed by positioning the static
pressure port in a depression in the surface of the vane, as
described above with respect to the first aspect.
As described with respect to the first aspect, preferably the first
static pressure system further comprises a first manifold internal
to the vane, wherein the first static pressure port is configured
to open into the first manifold, and wherein the first static
pressure conduit is configured to open into the first manifold and
configured to transmit a static pressure in the first manifold.
Preferably the first depression is a first groove that extends
along the first vane surface, and more preferably, the first groove
runs substantially parallel to the leading edge of the vane. While
preferable, other forms of depression which correct for a static
pressure defect are also foreseen.
As described with respect to the first aspect, the first pressure
system may comprise either one or two static ports. Further, the
vane may comprise a second static pressure system with one or two
ports, as described above.
Preferably each static port is located in a depression which
corrects a static pressure defect caused by air flowing over the
surface of the vane.
In certain preferable embodiments, the probe may further comprise
an electronics assembly, similarly to as described above with
respect to the first aspect.
According to a third aspect, there is provided a vehicle comprising
the moving-vane angle of attack probe according to either the first
or second aspect, wherein preferably the vehicle is an
aircraft.
BRIEF DESCRIPTION OF THE DRAWINGS
Some examples of moving-vane angle of attack probes according to
the invention will now be described with reference to the
accompanying drawings in which:
FIG. 1 is a perspective view of a moving-vane angle of attack probe
according to a first embodiment;
FIGS. 2A, 2B, and 2C are front, side, and rear end views
respectively of the moving-vane angle of attack probe shown in FIG.
1 with the electronics assembly omitted;
FIGS. 3A and 3B are cross-sectional and longitudinal sectional
views respectively of the moving-vane angle of attack probe shown
in FIGS. 1, and 2A to 2C;
FIG. 4 is an exploded perspective view of a moving-vane angle of
attack probe according to a second embodiment, with the electronics
assembly omitted;
FIG. 5 is a perspective view of the moving-vane angle of attack
probe of FIG. 4;
FIGS. 6A, 6B, and 6C are front, side, and rear end views
respectively of the moving-vane angle of attack probe shown in
FIGS. 4 and 5 with the electronics assembly omitted;
FIGS. 7A and 7B are cross-sectional and longitudinal sectional
views respectively of the moving-vane angle of attack probe shown
in FIGS. 4, 5 and 6A to 6C;
FIG. 8 is a perspective view of a moving-vane angle of attack probe
according to a third embodiment;
FIGS. 9A, 9B, and 9C are front, side, and rear end views
respectively of the moving-vane angle of attack probe shown in FIG.
8 with the electronics assembly omitted;
FIGS. 10A and 10B are cross-sectional and longitudinal sectional
views respectively of the moving-vane angle of attack probe shown
in FIGS. 8, and 9A to 9C; and
FIG. 11 is a graph showing the coefficient of pressure at points
along one side of the moving-vane angle of attack probes shown in
FIGS. 4 to 10B.
DETAILED DESCRIPTION
The moving-vane angle of attack probe shown in FIGS. 1 to 3B
comprises a vane 1. The vane 1 is made up of a leading edge 1a,
trailing edge 1b, and first and second vane surfaces 1c, 1d that
extend between the leading edge and the trailing edge on opposing
sides to define the vane. The first and second vane surfaces meet
at a top edge 1e of the vane 1, the top edge extending from a first
end of the leading edge 1 to a corresponding first end of the
trailing edge 1b. In alternative embodiments, a top edge surface
may instead extend between the first and second vane surfaces along
the top edge. The vane is closed along a bottom edge 1f by a bottom
edge surface that is substantially planar and covers an area
between the first and second vane surfaces 1c, 1d at a second end
of the leading and trailing edges 1a, 1b.
In this embodiment, the distance between the leading edge 1a and
trailing edge 1b in a direction parallel to the intended direction
of travel is approximately 100 mm. The height of the vane, which is
to say the distance between the top edge 1e and bottom edge 1f, in
a direction perpendicular to the intended direction of travel is
approximately 130 mm. The distance between the first and second
vane surfaces 1c, 1d varies between the leading edge and the
trailing edge, with the greatest distance between the two being
approximately 14.6 mm.
The vane 1 is connected to an electronics assembly 2 via a pivot 3
which extends through a top surface of the electronics assembly. An
integrally formed pivot attachment flange 3a (shown in FIG. 4)
extends from the bottom edge 1f of the vane, and connects the vane
to the pivot 3 such that the vane can pivot freely about an axis X
that is substantially perpendicular to the top and bottom edges 1e,
1f. The pivot 3 is located such that the axis of rotation X is
closer to the leading edge 1a than the trailing edge 1b. The pivot
3 allows the vane 1 to rotate as the assembly moves through the air
in order to align the leading and trailing edges 1a, 1b with the
oncoming wind so that the angle of attack may be determined.
The pivot 3 is connected to a shaft 13 which extends through the
electronics assembly 2, and is mounted on first and second bearings
13a, 13b at opposing inside walls of the electronics assembly. A
counterweight system 9 extends laterally from the shaft, fixed with
respect to the vane, and is configured to counter the mass of the
vane 1 which is primarily on one side of the axis X. The
electronics assembly is described in more detail below.
In this embodiment the vane is "swept back", which is to say that
leading edge 1a makes an angle with the axis of rotation X, and in
particular the leading edge runs along a direction which has a
component, perpendicular to the axis of rotation X, that points
towards the trailing edge 1b. The angle that the leading edge makes
with the axis of rotation provides that the vane can travel at
speeds of Mach 1 or higher by ensuring subsonic flow over the
leading edge in transonic and supersonic flight. Further, the swept
back configuration provides that of the centre of pressure is
located behind the axis of rotation, increasing the stability of
the vane. In this embodiment an angle of approximately 35.degree.
is used, however it will be appreciated that other angles will also
be suitable depending on the desired maximum operational speed.
In this embodiment, the trailing edge 1b extends substantially
parallel to the leading edge 1a such that the vane has a
substantially parallelogram shape when viewed in a side view.
However, in other embodiments, the trailing edge 1b may, for
example, be parallel to the axis of rotation X.
The moving-vane angle of attack probe according to the invention
further includes a total pressure system internal to the vane 1 for
determining a total pressure, which will now be described in
detail.
The leading edge 1a features an opening 4 on the leading edge of
the vane. In this embodiment, the opening 4 has a substantially
rectangular profile, and is configured so that the long edge of
said rectangle runs along the leading edge 1a to define a slot in
the leading edge 1a of the vane.
In this embodiment, the opening 4 has a length of approximately 48
mm along the leading edge, and a width of approximately 2 mm.
The opening 4 on the leading edge 1a opens into an interior chamber
5 located between the first and second vane surfaces 1c, 1d. The
interior chamber 5 runs from the leading edge 1a across the vane to
an exhaust opening 6 located in the trailing edge 1b. The opening 4
is thereby in fluid communication with said exhaust opening 6 via
the interior chamber 5.
In this embodiment, the exhaust opening 6 has a substantially
rectangular profile, and is configured so that the long edge of
said rectangle runs along the trailing edge 1b to define a slot in
the trailing edge 1b of the vane. In this embodiment, the exhaust
opening has a length of approximately 48 mm along the trailing
edge, and a width of approximately 3 mm.
The opening 4 and exhaust opening 6 have an area ratio of
approximately 4:6 (i.e. 96 mm.sup.2:144 mm.sup.2), which has been
found to be advantageous to obtain pressure recovery at low
airspeeds.
The interior chamber 5 is defined by four interior chamber walls
5a, 5b, 5c, 5d, which extend between the opening 4 and the exhaust
opening 6. The first and second opposing interior chamber walls 5a,
5b extend from the shorter sides of the opening 4 to the
corresponding shorter sides of the exhaust opening. The third and
fourth opposing interior chamber walls 5c, 5d extend from the
longer sides of the opening 4 to the corresponding longer sides of
the exhaust opening 6. The arrangement of the interior chamber
walls 5a, 5b, 5c, 5d results in the interior chamber having a
substantially rectangular cross-section.
At the mid-section of the interior chamber, where each interior
chamber walls is running substantially parallel to its opposing
wall, the distance between the first and second interior chamber
walls is approximately 20 mm in a direction perpendicular to the
direction of travel, and the distance between the third and fourth
interior chamber walls is approximately 3 mm, giving the interior
chamber a cross-sectional area of approximately 60 mm.sup.2.
However, as will be described below, large portions of this
cross-sectional area will be occupied by a pitot-tube along the
interior chamber.
The first and second interior chamber walls 5a, 5b are shaped so as
to curve in from the opening 4 before each running substantially
parallel to the top and bottom edges. The curve of first and second
interior walls reduces the distance therebetween as they proceed
from the opening 4 into the body of the vane, before the walls run
substantially parallel with each other towards the exhaust
opening.
The precise curvature of the first interior chamber wall 5a, which
is the wall closest to the bottom edge 1f of the vane, is selected
in response to the cross-flow that will exist along the leading
edge 1a of the vane as the vane travels at high speed through the
air. The curvature is configured to straighten the flow direction
of air entering the opening 4 so that the air speed and direction
inside the interior chamber are not distorted by the cross-flow
along the leading edge 1a which would act to introduce air into the
opening at an angle to the actual wind direction. The degree of
cross-flow along the leading edge will depend on, in particular,
the angle which the leading edge makes with the intended direction
of travel. The curvature must therefore be selected based on the
shape of the vane in order to achieve the above described
straightening effect.
In this embodiment, the second interior chamber wall 5b, which is
the wall closest to the top edge 1e of the vane, is also curved,
however this is not essential to preventing a distortion due to
cross-flow. Instead, a curved second interior chamber wall is
preferable to, for example, a sharp angle between the leading edge
1a and the second interior chamber wall 5b as a curved surface
helps prevent icing occurring in the region of the opening 4. The
precise curvature of the second interior chamber wall 5b is
selected to ensure the smooth flow of air into the interior
chamber.
As mentioned above, the first and second interior chamber walls 5a,
5b curve in from the opening 4 and then run substantially parallel
to each other towards the exhaust opening 6 located on the trailing
edge 1b. In this embodiment, after running substantially parallel
across most of the width of the vane, the first and second interior
chamber walls 5a, 5b are then configured to taper outwards as they
approach exhaust opening 6.
The third and fourth interior chamber walls 5c, 5d are, for the
most part, planar between the opening 4 and the exhaust opening 6,
and substantially parallel with each other. However, the third and
fourth interior chamber walls 5c, 5d taper away from each other as
they proceed from the opening 4 into the body of the vane to
increase the distance therebetween from 1.5 mm, as it is at the
opening 4, to 3 mm, as it is along the majority of the interior
chamber.
As part of the total pressure system, a pitot-tube 8 is located
inside the interior chamber 5 defined by the four interior chamber
walls as described above. While a conventional, cylindrical
shielded pitot-tube may be placed inside the chamber, the inventor
has identified a preferable pitot-tube arrangement, used in this
embodiment and discussed in more detail below.
Because the vane is configured to rotate about an axis X, the
rotational symmetry of a conventional shileded pitot-tube is no
longer necessary since the direction of air flow will lie in a
plane that is parallel to the vane. Any direction of air flow other
than this would cause the vane to rotate until the direction of air
flow was once again parallel with this plane. Embodiments may
therefore instead use a "two-dimensional" pitot-tube.
Here a two-dimensional pitot-tube refers to a pitot-tube that does
not exhibit rotational symmetry and, more specifically, one which
is described by extrusion of a two-dimensional design.
The two-dimensional pitot-tube 8 is located in the interior chamber
5, with the front-most part of the pitot-tube being located spaced
back from the opening 4, at a position in-between the first and
second interior chamber walls as they begin to run parallel with
each other. The pitot-tube 8 comprises first and second shielding
walls 8a, 8b which run in parallel with each other and
substantially parallel with the first and second interior chamber
walls 5a, 5b, in a direction along the interior chamber 5. The
first and second shielding walls 8a, 8b are spaced apart from each
other, the first shielding wall 8a being closer to the first
interior chamber wall 5a, and the second shielding wall 8b being
closer to the second interior chamber wall 5b. Each shielding wall
extends from the third interior chamber wall 5c to the fourth
interior chamber wall 5d to define three separated channels in the
interior chamber 5. The first and second shielding walls define a
pitot-tube opening 8c therebetween, the pitot-tube opening
substantially facing the opening 4. The pitot-tube opening is
centred approximately 80 mm above the bottom edge of the vane 1f. A
pitot-tube rear wall 8d extends from the first shielding wall 8a to
the second shielding wall 8b, and from the third interior chamber
wall 5c to the fourth interior chamber wall 5d at a position spaced
back from the pitot-tube opening 8c to close the channel between
the two shielding walls and allow for the total pressure to be
sampled between the two shielding walls 8a, 8b. First and second
bypass channels 14a, 14b are defined between the first shielding
wall 8a and the first interior chamber wall 5a, and the second
shielding wall 8b and the second interior chamber wall 5b
respectively. The front-most ends of the shielding walls 8a, 8b
each narrow to a point so as to smoothly divide air flow to either
side, either into the pitot-tube opening or one of the first and
second bypass channels 14a, 14b. This arrangement of shielding
walls 8a, 8b defining a pitot-tube opening 8c and first and second
bypass channels effectively allows the pitot-tube to sample a
central, relatively uniformly flowing portion of the air moving
through the interior chamber 5 while allowing the more turbulent
air near the sidewalls to pass through the bypass channels 14a, 14b
to the exhaust opening 6.
The distance between the first and second interior chamber walls
5a, 5b and the respective first and second shielding walls 8a, 8b
is approximately 4 mm, giving the bypass channels a cross-sectional
area of approximately 12 mm.sup.2. Each shielding wall extends
another approximately 4 mm away from their respective first and
second interior chamber wall, leaving approximately 4 mm
therebetween which defines the pitot-tube opening 8c, which
therefore also has a cross-sectional area of approximately 12
mm.sup.2.
The cross-sectional area of the bypass channels result in a ratio
of the area of the opening to the area of each bypass channel of
4:1, and a ratio of the area of the exhaust opening to the area of
each bypass channel of 6:1. These area ratios are particularly
advantageous because the former allows a convergent inlet for flow
straightening without causing stalling of the air flow in the
bypass channels 14a, 14b, and the latter allows a divergent outlet
for pressure recovery to ambient pressure.
The pitot-tube 8 further comprises a solid end 8e located behind
the rear wall 8d, between the two bypass channels 14a, 14b which is
aerodynamically shaped and extends towards the exhaust opening
6.
A total-pressure sensor port 10 opens into the channel between the
first and second shielding walls 8a, 8b of the pitot-tube 8 from
either of the third or fourth interior chamber walls 5c, 5d. While
in this embodiment the port opens from the third or fourth interior
chamber wall, it will be appreciated that the port could also be
located in either the first or second shielding walls 8a, 8b. The
total-pressure sensor port 10 is a circular opening with diameter
of approximately 3 mm, and is connected via a total-pressure tube
10a to a pressure sensor 10c located in the electronics assembly 2.
The tube extends from the interior chamber wall 5c, 5d, internal to
the vane, to the pivot 3. The tube passes through the centre of the
pivot and the shaft 13 and into the electronics assembly 2. The
tube 10a communicates the pressure in the pitot-tube 8 to the
pressure sensor 10c, which is located on the counterweight system 9
in order to minimise the weight of the moving-vane angle of attack
probe as a whole.
In this embodiment, the vane includes the preferable feature of
drain holes 12. Each drain hole extends from the first or second
vane surface 1c, 1d to the respective third or fourth interior
chamber wall 5c, 5d such that it opens into the interior chamber at
a position between the two shielding walls 8a, 8b of the pitot-tube
8. In this embodiment the drain holes are located between the rear
wall 8d and the total-pressure sensor port 10. The drain holes act
to remove ingested water and melted ice from the pitot-tube 8. Each
drain hole has a circular cross-section and is approximately 0.6 mm
in diameter.
The electronics assembly will now be described in more detail with
particular reference to FIGS. 3A and 3B. In this embodiment, the
electronics assembly comprises a substantially cylindrical housing
2a located below the bottom edge 1f of the vane 1. As described
above, the shaft 13 runs through the electronics assembly,
coaxially with the cylindrical housing, and is mounted therein by
bearings 13a, 13b located on the upper and lower internal surfaces
of the housing 2a. The shaft 13 extends through the upper surface
of the electronics assembly housing to connect to the vane 1 via
pivot 3 so that the shaft rotates as the vane rotates.
A high resolution rotary encoder 15 is positioned approximately
halfway down the length of the shaft 13 and is configured to
accurately and precisely determine the angle of attack by detecting
the rotational position of the shaft. While a high resolution
rotary encoder 15 is used in this embodiment, other means may be
used for detecting the rotation of the shaft, including for example
a resolver.
An air-data computer 16 is located below the encoder 15, stationary
relative to the electrical assembly housing 2a, and is configured
to receive and process the readings from the encoder to determine
the angle of attack. The air-data computer further comprises a
connector 16a which allows the electronics assembly to be connected
to and communicate with external electronics such as, for example,
other moving-vane angle of attack probes.
As mentioned above, the electronics assembly 2 further houses a
counterweight system 9. The counterweight system 9 is fixedly
connected to the shaft 13 and comprises at least one counterweight
arm 9a, which extends away from the shaft, and hence the axis of
rotation X, in a direction opposite to the direction the vane
extends from the axis of rotation. The counterweight system further
has a counterweight mass 9b at the end of the counterweight arm 9a.
The mass distribution of the arm and counterweight are configured
to substantially balance the mass distribution of the vane relative
to the axis of rotation X.
In this embodiment, the pressure sensor 10c is located on the
counterweight system 9 so that the mass of the sensor can be used
to contribute to balancing the mass of the vane 1. Further, because
the counterweight system 9 rotates as the vane rotates, the need
for leakage-prone pneumatic rotary joints is removed. The pressure
sensor 10c sits on a second counterweight arm 9c which extends from
the shaft 13 directly below the first counterweight arm 9a. As
mentioned above, tube 10a connects the port 10 to the pressure
sensor 10c. In this embodiment, the tube 10c passes through the
centre of the pivot into the electronics assembly 2 where it passes
through the counterweight arm 9a and down to connect with the
pressure sensor 10c mounted directly below, on the second
counterweight arm 9c. To minimise the length of the tube 10a, the
counterweight system 9 is mounted at the very top of the shaft 13,
with the encoder 15 and the air-data computer 16 mounted below. The
pressure signal from the pressure sensor 10c is transferred to the
air-data computer 16 through slip rings 17 mounted on the shaft 13,
directly below the second counterweight arm 9c.
The construction and de-icing system of the embodiment of FIGS. 1
to 3B will now be discussed in more detail with reference to FIG.
4. FIG. 4 shows a multi-piece construction of a second embodiment
of the invention. The features of the second embodiment not present
in the first embodiment will be discussed in more detail below,
however the general principles of the construction of the second
embodiment, and the de-icing system are the same as in the first
embodiment, and it is these that will now be discussed.
It is imperative that, in use, the vane 1 and in particular the
pitot-tube are de-iced. In the present embodiment, the vane 1 is
formed from three distinct parts. First and second vane parts 101c,
101d form the first and second vane surfaces 1c, 1d respectively. A
third vane part 101a is made up of the leading and trailing edges
1a, 1b; top edge 1e; bottom surface 1f; pivot attachment flange 3a;
and the integrally formed opening 4, interior chamber 5, exhaust
opening 6, pitot-tube 8 and tube 10c. The first and second vane
parts 101c, 101d are placed on respective sides of the third vane
part 101a to form the vane 1.
The de-icing system comprises first and second foil heaters 210a,
210b which line the underside of the first and second vane parts
101c, 101d, i.e. the first and second vane surfaces 1c, 1d,
respectively. The de-icing system further comprises first and
second ceramic heaters 211a, 211b which sit on either side of the
third vane part 101a, facing the underside of the first and second
vane parts respectively. Specifically, the ceramic heaters extend
over the area of the interior chamber, adjacent to the third and
fourth interior walls 5c, 5d, respectively. Each of the heaters is
connected via wires (not shown) through the pivot into the
electronics assembly. When assembled, the ceramic heaters 211a,
211b are located in cut-outs 210c, 210d in the foil heaters 210a,
210b. This arrangement of heaters is particularly advantageous for
reducing the energy required for de-icing the vane 1.
The first embodiment represents an integrated sensor for
determining both the angle of attack, based on the rotational
position of the vane, and the total pressure, based on the air
pressure in the pitot-tube 8. While it is advantageous to integrate
these two sensors into a single assembly, in order to calculate,
for example, the Mach number, the static pressure as well as the
total pressure must be known. It is therefore particularly
advantageous for the moving-vane angle of attack probe to further
include static pressure sensors.
The second embodiment of the invention, shown in FIGS. 4 to 7B,
will now be described. The embodiment of FIGS. 4 to 7B is largely
the same as the embodiment of FIGS. 1 to 3B, and the same reference
numerals for identical features will be adhered to. The moving-vane
angle of attack probe of this embodiment differs in that a
pitot-static system is incorporated into the vane rather than a
pitot-tube. The pitot-static tube is largely the same as the
pitot-tube 8 of the first embodiment, but additionally includes a
first and preferably a second static pressure system 81, 82.
The static pressure systems are ideally to be used to determine the
freestream pressure, which is the air pressure upstream of the
vane, i.e. before the air pressure has been affected by the
movement of an aerodynamic body. However, in reality the static
pressure in the region of the vane will be affected by a number of
factors. Firstly, the static pressure in the region of the vane
will be affected by the movement of the body on which the vane is
mounted, for example, the fuselage of a plane. Secondly, the static
pressure in the region of the vane will be affected by the way in
which the air flows over the vane itself. Finally, the static
pressure in the region of the vane will be affected in a scenario
in which the angle of the vane lags behind a change in wind
direction. As described below, the second embodiment of the
invention features a number of design considerations made to
minimise or correct for these effects on the static pressure.
The first and second static pressure systems 81, 82 comprise first
and second manifolds 81c, 82c respectively, which in this
embodiment are located behind the rear wall 8d, internal to the
rear end 8e of the pitot-tube 8 so that said manifolds 81c, 82c are
isolated from the rest of the interior chamber 5. The manifolds are
defined by a rectangular cut-out made in the rear end 8e, which is
then closed on either side by the third and fourth interior chamber
walls 5c, 5d. The manifolds each have dimensions of 4 mm.times.7
mm.times.15 mm. The first manifold 81c is located directly behind
the rear wall 8d of the pitot-tube 8, and the second manifold 82c
directly behind the first manifold 81c such that the pitot-tube
opening 8c and the first and second manifolds 81c, 82c are located
at substantially the same height between the top edge 1e and bottom
surface of the vane 1f.
Each static pressure system 81, 82 further comprises a pair of
static ports 81a, 81b, 82a, 82b. The first static pressure system
81 features a first static port 81a, which extends from the first
vane surface 1c, through the vane to the third interior chamber
wall 5c to connect the manifold to the atmosphere. The first static
pressure system 81 further features a second static pressure port
81b which extends from the second vane surface 1d, through the vane
to the fourth interior chamber wall 5d to connect the manifold to
the atmosphere on the other side of the vane. Each of the first and
second static ports 81a, 81b is a circular opening with diameter of
approximately 2 mm. The second static pressure system 82 is
constructed similarly to the first 81, with first and second static
ports 82a, 82b on each side of the vane. By providing first and
second static ports connecting each manifold to the atmosphere on
either side of the vane, the air pressure in each manifold 81c, 82c
is an average of the pressure on either side of the vane 1 and so
the effects on the static pressure caused by the rotation of the
vane lagging behind a change in wind direction is cancelled
out.
It should also be noted that the static ports 81a, 81b, 82a, 82b
are at substantially the same height between the top edge 1e and
bottom surface of the vane 1f as the pitot-tube opening 8c. This is
advantageous because any effects on the static pressure will be
approximately equal for any pressure readings. Further, it is noted
that in this embodiment, the pitot-static tube is located closer to
the top edge 1e, than the bottom edge, which likely increases the
distance between the sensors and a body on which the vane assembly
is to be mounted, thereby reducing the effect of the body on the
static pressure in the region of the pitot-static tube. While it is
advantageous to place the sensors as far from the base as possible,
this will not entirely remove the effect of the body on the static
pressure. For the present embodiment, the remainder of the pressure
defect caused by the body on which the vane is to be mounted must
be corrected mathematically on a case-by-case basis depending on
the aerodynamic properties of the body.
Each static pressure system 81, 82 further comprises a static
pressure sensor port 110a, 110b located in the respective manifold
81c, 82c. Similarly to the pressure port 10, each static pressure
sensor port 110a, 110b opens into the manifold from one of the
third and fourth interior chamber walls 5c, 5d, and preferably all
three ports 10, 110a, 110b open from the same one of the third and
fourth interior chamber walls.
Each static pressure sensor port 110a, 110b communicates with a
respective static pressure tube 110c, 110d, which is similar to the
total-pressure tube 10a which connects to the total-pressure sensor
port 10. The static pressure tubes each communicate the pressure in
the manifold to a respective static pressure sensor 110e, 110f
located in the electronics assembly 2. The static pressure tubes
110c, 110d extend from the interior chamber wall 5c, 5d, internal
to the vane, to the pivot 3. The tubes pass through the centre of
the pivot and into the electronics assembly 2. The tubes 110c, 110d
each communicate the pressure in their respective manifold 81c, 82c
to a respective static pressure sensor 110e, 110f which is located
on the counterweight system 9.
As can be seen in FIG. 7A, the counterweight system 9 now has three
pressure sensors 10c, 110e, 110f located on the counterweight arm
9a. In this embodiment, the pressure sensors are spaced along the
counterweight arm at different radial distances from the shaft 13.
Each pressure sensor determines the air pressure at their
respective total-pressure or static pressure sensor port(s), with
each reading being passed to the air-data computer 16 via slip
rings 17.
As mentioned above, the static pressure in the region of the vane 1
will also be affected by the shape of the vane itself.
Specifically, as the leading edge deflects air around the vane, the
static pressure at the first and second vane surfaces 1c, 1d will
be reduced with respect to the freestream pressure. While it is
possible to correct for this pressure reduction mathematically,
this is made difficult, in part because a defect caused by the
aerodynamic body on which the vane is to be mounted must also be
corrected mathematically. In this embodiment, the vane is shaped to
counteract this reduction in pressure and to correct for the
pressure defect by design.
As shown in particular in FIG. 7A, the first and second vane
surfaces are shaped such that each static port 81a, 811b, 82a, 82b
opens through the first or second vane surface 1c, 1d at the bottom
of a shallow depression. Each depression corresponds to a separate
groove 181, 182 formed in the surface of the vane, with each groove
running up the vane between the bottom edge if and top edge 1e.
Each vane surface 1c, 1d therefore has two shallow grooves 181, 182
corresponding to each static port. The precise width of each
groove, depth of each groove, and angle each groove makes with the
axis of rotation is selected aerodynamically to correct for the
pressure defect caused by the shape of the vane at the position of
each static port 81a, 81b, 82a, 82b. These grooves will remove this
defect for all airflow speeds, and leave only a defect due to the
aerodynamic body on which the vane is to be mounted requiring
mathematical correction. In this embodiment, the vane dimensions
are the same as in the first embodiment, and groove dimensions of
length 115 mm (measured parallel to the leading edge), depth 1 mm,
and width 15 mm (measured along the chord of the vane) were found
to correct for the shape of the vane.
FIG. 11 is a graph showing how the shaping of the vane affects the
coefficient of pressure at points along the surface of the vane.
This demonstrates that the depressions, and placement of static
ports within the depressions, can be configured such that the
coefficient of pressure is approximately zero in the region of each
static port.
In a third embodiment of the invention, a vane is provided with the
first and second static pressure systems only, as shown in FIGS. 8
to 10B.
In this embodiment, the vane is of substantially the same external
shape as in the first two embodiments, but does not have an
opening, interior chamber, or exhaust opening. In this embodiment,
the first and second static pressure systems 281, 282 comprise
first and second manifolds 281c, 282c respectively. The first and
second manifolds are cuboidal chambers located inside the vane.
Each static pressure system 281, 282 further comprises a pair of
static ports 281a, 281b, 282a, 282b. The first static pressure
system 281 features a first static port 281a, which extends from
the first vane surface 1c, through the vane to the first manifold,
thereby connecting it to the atmosphere. The first static pressure
system 281 further features a second static pressure port 281b
which extends from the second vane surface 1d, through the vane to
the first manifold, thereby connecting it to the atmosphere on the
other side of the vane.
The second static pressure system 282 is constructed similarly to
the first 281, with first and second static ports 282a, 282b on
each side of the vane. By providing first and second static ports
connecting each manifold to the atmosphere on either side of the
vane, the air pressure in each manifold 281c, 282c is an average of
the pressure on either side of the vane 1 and so the effects on the
static pressure caused by the rotation of the vane lagging behind a
change in wind direction is cancelled out.
It should also be noted that the static ports 281a, 281b, 282a,
282b are at substantially the same height between the top edge 1e
and bottom edge of the vane 1f, i.e. both are approximately 80 mm
above the bottom edge of the vane. This is advantageous because any
effects on the static pressure caused by an aerodynamic body to
which the vane is mounted will be approximately equal. Further, it
is noted that in this embodiment, the static ports 281a, 281b,
282a, 282b are located closer to the top edge 1e, than the bottom
edge, which likely increases the distance between the static ports
and a body on which the vane assembly is to be mounted, thereby
reducing the effect of the body on any pressure readings. While it
is advantageous to place the static ports as far from the base as
possible, this will not entirely remove the effect of the body on
the static pressure. As in the second embodiment, the remainder of
the pressure defect caused by the body on which the vane is to be
mounted must be corrected mathematically on a case-by-case basis
depending on the aerodynamic properties of the body.
Each static pressure system 281, 282 further comprises a static
pressure sensor port 210a, 210b located in the respective manifold
281c, 282c. Each static pressure sensor port 210a, 210b opens into
the respective manifold through one of the manifold walls.
As in the second embodiment, each static pressure sensor port 210a,
210b communicates with a respective static pressure tube 210c,
210d. The static pressure tubes each communicate the pressure in
the manifold to a respective static pressure sensor 210e, 210f
located in the electronics assembly 2. The static pressure tubes
210c, 210d extend from the respective manifold, internal to the
vane, to the pivot 3. The tubes pass through the centre of the
pivot and into the electronics assembly 2. The tubes 210c, 210d
each communicate the pressure in their respective manifold 281c,
282c to a respective static pressure sensor 210e, 210f which is
located on the counterweight system 9.
As can be seen in FIG. 10A, the counterweight system 9 now has two
pressure sensors 210e, 210f located on the counterweight arm 9a. In
this embodiment, the pressure sensors are spaced along the
counterweight arm at different radial distances from the shaft 13.
Each pressure sensor determines the air pressure at their
respective static pressure sensor ports, with each reading being
passed to the air-data computer 16 via slip rings 17.
As mentioned above, the static pressure in the region of the vane 1
will also be affected by the shape of the vane itself.
Specifically, as the leading edge deflects air around the vane, the
static pressure at the first and second vane surfaces 1c, 1d will
be reduced with respect to the freestream pressure. While it is
possible to correct for this pressure reduction mathematically,
this is made difficult, in part because a defect caused by the
aerodynamic body on which the vane is to be mounted must also be
corrected mathematically. In this embodiment, the vane is shaped to
counteract the reduction in pressure caused by the vane itself,
thereby correcting for this pressure defect by design.
As shown in particular in FIG. 10A, the first and second vane
surfaces are shaped such that each static port 281a, 282a opens
through the first or second vane surface 1c, 1d at the bottom of a
shallow depression. Each depression corresponds to a separate
groove 181, 182 formed in the surface of the vane, with each groove
running up the vane between the bottom edge 1f and top edge 1e.
Each vane surface 1c, 1d therefore has two shallow grooves 181, 182
corresponding to each static port. The precise width of each
groove, depth of each groove, and angle each groove makes with the
axis of rotation is selected to aerodynamically correct for the
pressure defect caused by the shape of the vane at the position of
each static port 281a, 282a. These grooves will remove this defect
for all airflow speeds, and leave only a defect due to the
aerodynamic body on which the vane is to be mounted requiring
mathematical correction. Grooves shaped and positioned as described
with reference to the second embodiment were found to correct for
the static pressure defect caused by the air flowing over the
vane.
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